Surge diverter units comprising spark gaps shunted by resistive blocks



April 11, 1967 A D. MILLER 3,313,978

SURGE DIVERTER IjNITS COMPRISING SPARK GAPS SHUNTED BY RESISTIVE BLOCKS Filed Aug. 31, 1964 Fig.1

5 1 I u c 8 0 9 4 Fi .2; 11 El 12 1 v I (4L r7jf [15 United States Patent 3,313,978 SURGE DIVERTER UNITS COMPRISING SPARK GAPS SHUNTED BY RESISTIVE BLOCKS Alan David Miller, Wigan, England, assiguor to Associated Electrical Industries Limited, London, England, a British company Filed Aug. 31, 1964, Ser. No. 393,044 Claims priority, application Great Britain, Sept. 3, 1963, 34,830/ 63 Claims. (Cl. 315-36) This invention relates to surge diverter units including a spark gap and resistance connected in series.

Surge diverters can be made up of a number of such units stacked one on top of another, and in order to obtain a predetermined voltage distribution acrossthe several spark gaps it is usual for these gaps to be electrically shunted by linear or non-linear resistances.

It is an object of theinvention to provide an improved form of surge diverter unit which includes such grading resistance.

According to the invention, there is provided a surge diverter unit in which a spark gap assembly accommodated in the bore of an annular block of ressitance material is connected in series between resistive elements formed by two circumferentially spaced portions of the spark gap assembly is preferably connected between the two portions forming the series elements by means of connections made to said portions on opposite faces of the annular block.

In order that the invention may be more fully understood a surge diverter unit embodying the invention will now be described, by way of example, with reference to the accompanying drawing in which:

FIG. 1 represents in plan view a surge diverter unit in accordance with the invention;

FIG. 2 is a part sectional elevation of a portion of a multiple unit surge diverter built up from units as shown in FIG. 1; and

FIG. 3 represents the equivalent electrical circuit of the unit shown in FIG. 1.

Referring in the first instance to FIGS. 1 and 2, the

surge diverter unit comprises a unitary block 1 of nonlinear resistance material having an annular form and on both annular faces 3 and 4 of which are 'two diametrically opposed non-contiguous arc'uate conductive layers 2A and 2C on face 3 and 2B and 2D on face 4. These layers can be formed for instance by brass or copper sprayed on to the relevant parts of the surfaces 3 and 4 of the block 1. A spark gap assembly comprising two spaced electrodes 5 and 6 defining a spark gap G is accommodated in the bore 7 of the block, the electrode 5 being carried by a support member 8 which electrically connects it to the conductive layer 2B and the electrode 6 being carried by a support member 9"which electrically connects it to the conductive layer 2C. This simple form of spark gap assembly is shown only by way of example and more complex assemblies may be used instead. An insulating tube 10 may be fitted in the bore 7 of the block 1 to prevent arcing between the bore 7 and the electrodes 5 and 6. Such a tube 10 is not essential to the simple spark gap assembly shown but may be necessary with a more complex spark gap assembly. As

ICC

will be appreciated from reference to FIG. 3, the electrical circuit of the unit comprises two resistive elements RD which are respectively formed by the circumferentially spaced portions of the block 1 sandwiched between the conductive layers 2A and 2B on the one hand and between the conductive layers 2D and 20 on the other hand. These two resistive elements are connected in series with the spark gap by virtue of the connection of the conductive support members 8 and 9 to the layers 2B and 2C respectively. Further, grading resistive elements RG shunting the spark gap G are constituted by the portions 11 of the block between the portions sandwiched by the conductive layers 2. These grading resistive elements RG are arranged to have a resistance value much higher than that of the resistive elements RD, for instance by making the portions 11 of the block of smaller crosssectional area than that of the remainder of the block 1 or in any other manner not shown).

As illustrated in FIG. 2 a number of units can be assembled together to form a multiple unit surge diverter by stacking them one above the other with intervening insulating plates such as 12, and connecting them in series by means of conductive members such as 13 which pass through the insulating plates 12 and establish electrical connection between the conductive layer 2D on one block and the conductive layer 2A on an adjacent block in the stack. In use, with the spark gaps non-conducting, a small current flows through the resistive elements RD and RG of all the units in series, and if the resistive elements RG are substantially equal in value a substantially uniform distribution of voltage across the spark gaps is obtained. Other resistive elements such asRg Rg and Rg (shown in dotted line) which include the portions 11 of the block, contribute to the voltage distribution. When the spark gaps are conducting, most of the current flows axially through the blocks 1 and spark gaps as indicated by the arrows in FIG. 2, so that each block acts as two electrically independent resistors RD connected in series by the spark gap as in FIG. 3.

Surge diverter units in accordance with the invention are advantageous in that sepaarte grading resistors do not have to be accommodate in the bore 7, and therefore the whole of the bore can be utilised to accommodate the spark gap. Moreover as the grading resistive elements are incorporated in the mass of the block 1 and this mass is greater than that of conventional grading resistors the possibility of overheating during short term voltage surges is considerably reduced.

Depending on the resistance characteristics required, and in particular on the relationship required between the resistances RD and RG provided by the series and shunt portions of the block 1, the material of the block may be homogenous throughout or the material of the grading resistance portions 11 of the block may suitably differ from that of the remainder of the block 1 in respect of its resistancecharacteristics. For instance the portions 11 of the block may have a linear resistance characteristic while the remainder has a non-linear characteristic.

gap assembly in series with said series resistive element portions, and shunt resistive elements for the spark gap assembly constituted by the portions of the block of higher resistance between the first-mentioned portions.

2. A surge diverter unit as claimed in claim 1 wherein the connections connecting the spark gap assembly to the series resistive element portions of the block are connected to said portions at opposite faces of the block.

3. A surge diverter unit as claimed in claim 1 included with a number of similar units in a stack constituting a multiple unit surge diverter, said diverter including connections connecting the several units of the stack in series.

4. A surge diverter unit comprising an annular block of resistance material, two diametrically opposed noncontiguous conductive layers on each annular face of the block, a spark gap assembly accommodated in the bore of the block, and connections from said assembly to diametrically opposed conductive layers on opposite faces of the block, said connections connecting the spark gap assembly in series with the portions of the block sandwiched between layers, so that said portions thereby constituting series resistive elements of the unit, while the portions of block between the sandwiched portions constitute shunt resistive elements shunting the spark gap assembly.

5. A surge diverter unit as claimed in claim 3 included with a number of similar units in a stack constitutinga multiple unit surge diverter, said diverter including between each pair of adjacent units an insulating member insulating the units from each other and a connecting member engaging on the facing faces of the two units of the pair the conductive layers thereon other than those to which the connections from the spark gap assemblies are made. I

References Cited by the Examiner UNITED STATES PATENTS 4/1959 Rabus 315-36 3/1964 Rabus 31536 

1. A SURGE DIVERTER UNIT COMPRISING A UNITARY ANNULAR BLOCK OF RESISTANCE MATERIAL, A SPARK GAP ASSEMBLY ACCOMMODATED IN THE BORE OF SAID BLOCK, SERIES RESISTIVE ELEMENTS FOR THE UNIT CONSTITUTED BY TWO CIRCUMFERENTIALLY SPACED PORTIONS OF THE BLOCK, CONNECTIONS CONNECTING THE SPARK GAP ASSEMBLY IN SERIES WITH SAID SERIES RESISTIVE ELEMENT PORTIONS, AND SHUNT RESISTIVE ELEMENTS FOR THE SPARK GAP ASSEMBLY CONSTITUTED BY THE PORTIONS OF THE BLOCK OF HIGHER RESISTANCE BETWEEN THE FIRST-MENTIONED PORTIONS. 